I need a new bike. Any suggestions would be great.

I own a older diamondback mountain bike now that has seen better days and I plan on buying something new soon. I want a good bike at a good price. I know you can buy bikes starting at $100 to thousands of dollars. I want something with a moderate cost but good quality, until I am sure I will use the bike enough to justify paying more money. Any suggestions would be much appreciated.

Pick a price range and go from there. Most decent hardtails will run you between 400 to 600 USD and fs will run you between 800 to 1200 depending on yr/mk/components. You can get bikes cheeper but if you plan on doing any serious riding I would not suggest it.
Slainte

The Diamondback I own now is a rigid bike (no Suspension). I assume these bikes have gone the way of the dinosaur? The hardtail sounds like what I am looking for. Anyone got suggestions on a good hardtail at around $300-600?

Closer to 600 and you can basicaly just pick one from a reputable company. I prefer Kona or Giant but any of the major companies will have a good bike with decent components. The most important consideration is fit. Find the one that fits you and you'll be good to go. Try to find a good LBS that is not just interested in sales and ask them for help.
Slainte

looks like you're in the right direction... l can't recommend anything specific, but i would look for a used quality hardtail at best 1-3 years old - or a new one is you find a good deal.

DO NOT buy a full suspension for less than say $600 -- i personally wouldn't go FullSuspension for less than $1000... cheap FS are heavy and have inefficient pedalling --- unless you're doing special riding (like downhill only) ONLY buy a 4-bar-linkage rear-suspension (like Specialized FSR, Trek Fuel, Giant NRS, etc) -- most others have too much rear "bob"

i personally am a fan of buying a slightly used top-of-the-line bike rather than a cheaper new one...

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